1. Field of the Invention
The present invention relates broadly to stud welding guns used for arc-welding of metallic studs to a work plate. More particularly, it is concerned with an improved, relatively permanent operating head for such guns which include as a feature thereof means for fluid cooling of the head in order to increase the useful life thereof and eliminate the need for ferrule replacement after each welding operation.
2. Description of the Prior Art
A number of stud welding guns have been proposed in the past. These units are used to arc-weld relatively short, cylindrical studs onto a metallic work piece, e.g., a boiler plate. In many prior stud welding guns, a ceramic ferrule is provided which is annular in configuration and engages the work piece and surrounds the end of the stud during the welding sequence. The ferrule serves to confine molten metal to the immediate vicinity of the weld, as an indexing means, and as a safety collar. A persistent problem encountered with such ceramic ferrules is that they can be normally employed for only a single welding sequence. This occurs because the ceramic material of the ferrule can react with the molten metal produced at the weld area, thereby rendering the ferrule unusable. Moreover, the brittle nature of ceramic ferrules renders them prone to cracking during the welding operation. For all of these reasons, the general practice is to simply break away and discard the ceramic ferrule after each operation, followed by replacement with a new ferrule. As can be appreciated, this is an expensive and time consuming task, and therefore a truly permanent operating head for stud welding guns would represent a significant advance in the art.
The following patents are directed to various aspects of known stud welding guns: U.S. Pat. Nos. 3,597,572, 3,555,238, 3,557,339, 3,582,602, 3,790,740, 3,309,495, 3,408,472, 3,662,145, 3,723,700, 4,002,876, and 4,027,136.
Patent No. 3,557,339 relates to a reusable welding ferrule formed of a nonconsumable material such as graphite which has a tapered work end and a series of circumferentially spaced notches. The patent is not concerned with provision of fluid cooling structure for the ferrule in order to increase the life thereof.
U.S. Pat. No. 3,555,238 to Fay et al. describes a permanent arc shield formed of an electrically conductive material such as boron nitrite. A water cooling assembly is disclosed in conjunction with this arc shield which is of relatively bulky nature and would in effect preclude use of this type of operating head in the case where relatively closely spaced studs must be installed or replaced.
U.S. Pat. No. 4,002,876 is directed to a stud welding tool having a specialized retraction mechanism, but discloses a so-called permanent arc shield. Again however, no fluid cooling apparatus is provided with this arc sheild.
U.S. Pat. No. 3,790,740 is concerned with a welding gun using a ceramic ferrule with means for creating a rotary or cyclonic flow of air adjacent the weld area.
The remaining patents listed above are directed to various details of known stud welding guns, and therefore are not directly pertinent to the instant invention.